Determining the potential human exposure to contaminants associated with Superfund sites requires an understanding of the persistence and movement of these contaminants in all environmental media. This Project is centered on assessment of human exposure to contaminants, with particular emphasis on determining how environmental fate and transport processes control the level and duration of such exposure. We will investigate basic physical, chemical, and biological processes, and their interactions, contributing to variability in fate and transport of contaminants in the vadose zone, groundwater, and surface water, and describe these processes in mathematical simulation models. Another important area is the development of approaches for monitoring bioremediation and establishment of appropriate cleanup levels. Particular emphasis will be on biodegradation of contaminants by microbes, both at the genomic/proteomic level in specific strains, as well as application of bioremediation technologies at the field scale. We will develop molecular tools to quantify microbial populations in time and space by targeting phylogenic and functional genes;develop basic information on contaminant biodegradation pathways;and link contaminant biodegradation directly to specific populations and their densities. We will estimate the relative importance of coupled physical, chemical, and biological fate processes occurring at multiple scales across multiple media in contributing to exposure variability. We will use transport and fate models to integrate our knowledge of the different rate limiting processes and complexity into the RBCA (Risk Based Corrective Action) framework, providing a more reliable, realistic tool for cleanup analysis and design. Consideration of multimedia contaminant transport is critical for determining human exposure. Accordingly, a new thrust of this project is on the transport of contaminants via atmospheric and surface water pathways, including investigation of exposure to particulate-associated contaminants in surface water and in air. Extraction methods, analytical methods, and experimental results related to particle bound contaminants obtained here will benefit from and contribute to Projects. In cooperation with Ellen Gold, epidemiologists at the California Department of Health Services, and the Statistical Analysis Core, we propose to both develop the appropriate methods and explore the consequences using field epidemiological data from a contaminated site that has caused human exposure (e.g., Rancho Cordova perchlorate problem).